1. Field of the Invention
The present invention relates to a method for producing electrodes for all-solid battery and another method for producing all-solid battery.
2. Description of the Related Art
Secondary batteries are now used as the power source for recently prevailing machinery and tools, such as portable personal computers, mobile telephone terminals and other communication tools, domestic storage systems, hybrid automobiles, and electric vehicles. Among such secondary batteries are lithium-ion secondary batteries which have a higher energy density than other secondary batteries, such as nickel-hydrogen storage batteries. However, lithium-ion secondary batteries, which contain a flammable organic solvent as the liquid electrolyte, need a safety device to prevent firing and bursting caused by overcurrent due to short circuit. Moreover, on account of the necessity for such a safety device, they are sometimes restricted in selection of battery materials and design of battery structure.
To cope with the foregoing situation, efforts have been being made to develop all-solid batteries which contain a solid electrolyte in place of a liquid electrolyte. The all-solid batteries have an advantage that they only need a simpler safety device because of the absence of flammable organic solvent. Consequently, they are regarded as batteries superior in production cost and productivity. Moreover, they are expected to be promising batteries which are safe and yet have a high capacity and a high output because they can be easily connected in series owing to the structure including paired electrode layers (or cathode layer and anode layer) and a solid electrolyte layer held between such electrode layers.
The all-solid batteries are known to have the internal resistance which is greatly affected by the contact resistance that occurs between adjacent particles of an active material (for battery reactions) or between adjacent particles of the active material and solid electrolyte. A change in internal resistance results from the active material changing in volume after repeated charging and discharging. The active material with volume change then becomes loose in contact with the active material and solid electrolyte, which tends to increase internal resistance and decrease capacity. To tackle this problem, there have been proposed techniques to prevent the increase in internal resistance.
Regarding such techniques, JP-2003-059492-A discloses a lithium secondary battery in which at least either of the cathode and anode has active material particles which are coated with a coating layer containing a conductive material and a lithium ion conductive inorganic solid electrolyte.
JP-2013-134825-A discloses a composite active material having an active material and a coating layer formed thereon, the coating layer containing a carbonaceous substance and an ion-conductive oxide. The coating layer has a surface in which the concentration of carbon is no less than 17.0 atm %.